Ear infections are among the most common reasons for sick child visits to medical providers. Risk factors for otitis media have been identified in prior clinical studies, but epidemiologic studies of sufficient size to allow generalization to the wider community or national population have been less common. Our goal has been to extend this research by analyzing several U.S. national data sets, collected under the auspices of the National Center for Health Statistics, with support from NIH, and other available population-based datasets. In particular, we have examined the 1991 Longitudinal Follow-up (LF) to the 1988 National Maternal and Infant Health Survey (NMIHS). The NMIHS was over-sampled for black race and VLBW (less than 1500 g) and MLBW (1500-2499 g) children. The LF included a Medical Provider Survey (MPS) and a maternal questionnaire, both obtained when the children were approximately 3 years old. The number of episodes of otitis were documented based on the MPS. Risk factors were extracted from the maternal questionnaire and the original baseline NMIHS questionnaire. The factors found to have significant odds ratios (OR) with 95% confidence intervals (CI) with the outcome defined as frequent ear infections (3 or more episodes) were: VLBW [OR=1.40; CI=1.20,1.74] and any child care [OR=1.47; CI=1.28,1.68]. Although child care has been shown consistently to be associated with increased risk of otitis media, the association with very low birth weight has not been shown conclusively before, perhaps because of inadequate numbers of subjects in earlier studies. The present study did not find an association with maternal cigarette smoking in pregnancy or with household smoking after birth, unlike some earlier studies, but in agreement with still others. No association was demonstrated with moderately low birth weight (1500-2499 g) infants. In other studies we have addressed the frequency of "flat" tympanograms for children sampled approximately each six months through the first five years of life, based on the Children in Focus sample drawn from the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC). We have also examined risk factors for otitis from other longitudinal studies, including the Alabama and Scandinavian Successive Small-for-Gestational Age Birth Study. These two latter studies allow for the investigation of other outcomes in relation to frequent childhood ear infections, since children were examined using several cognitive tests at 5 years of age.